When a difference in retinal image between both eyes (binocular parallax), which is probably generated when an object is watched with both eyes, is nonrandomly produced in a display device, it is possible to make human eyes recognize a three-dimensional image. Various display devices for a three-dimensional image, which use this principle of binocular parallax, have been developed. The display devices for a three-dimensional image are broadly classified into a type with specific spectacles for binocular vision or a type without spectacles.
In the type with spectacles, there are a method of coloring right and left images with different colors and viewing the images while wearing spectacles with the reversed right and left colors, and a method of shooting right and left images with filters polarized at right angles to each other and viewing the images while wearing spectacles with filters respectively polarized in the same direction, for example, and various methods have been developed and commercialized. However, the type with spectacles for binocular vision is not able to eliminate the vexatious complication of wearing spectacles, and therefore the type without the spectacles has been becoming mainstream recently.
In the display devices for a three-dimensional image in the direct-sight type without spectacles, light from a pixel has a direction controlled with an optical system such as a parallax barrier, a lenticular lens, or a microlens array (fly's-eye lens) to reflect different images respectively onto right end left eyes and obtain a stereognostic sense.
For example, Patent Document 1 below discloses a technique of using a parallax barrier to reflect an image for right eye and an image for left eye onto a right eye and a left eye respectively for displaying a three-dimensional image.
Patent Document 1: Japanese Patent Laid-Open 8-036145 (page 2, FIG. 1)
The technique for displaying a three-dimensional image, which is described in the Patent Document 1 above, will be described in detail with reference to FIGS. 15 and 16. FIGS. 15 and 16 are diagrams showing a positional relationship of a pixel of a liquid crystal panel 1401, a parallax barrier 1403 with an aperture 1402 in the shape of a slit, and both eyes of a viewer.
Of a plurality of pixels of the liquid crystal panel 1401, FIGS. 15 and 16 show only sections of a line of pixels in the direction along a line connecting the both eyes. The aperture 1402 has a longitudinal direction that corresponds to a direction vertical to the direction along the line connecting the both eyes in a plane parallel to the liquid crystal panel.
The parallax barrier 1403 is positioned between the viewer and the liquid crystal panel 1401. On the opposite side of the liquid crystal panel 1401 from the viewer, a light guiding plate 1404 is provided, and light emitted from a light source 1405 is made to travel in the light guiding plate 1404 and irradiated to the liquid crystal panel 1401.
Then, when a three-dimensional image is displayed as shown in FIG. 15, two adjacent pixels in the direction along the line connecting the both eyes, of the liquid crystal panel 1401, are differently used as a pixel for right eye and a pixel for left eye respectively. In the pixel for left eye, an image that is probably obtained as viewed from the left eye (image L) is displayed, and an image that is probably obtained as viewed from the right eye (image R) is displayed in the pixel for right eye.
Accordingly, a portion of light emitted from the light guiding plate 1404 is transmitted through each pixel of the liquid crystal panel, and then through the aperture 1402 of the parallax barrier 1403 to enter the both eyes of the viewer. On this occasion, when the relation of a pitch B of the aperture 1402, a pixel pitch P of the liquid crystal panel 1401, and a distance E between the both eyes is optimized, it is possible to make light from the pixel for right eye incident only into the right eye and to make light from the pixel for left eye only incident into the left eye. In the result, it is possible to make the viewer recognize a three-dimensional image formed of the image L and the image R.
In the case of displaying a two-dimensional image, without using adjacent pixels in the direction along the line connecting the both eyes differently as the pixel for right eye and the pixel for left eye respectively, the same image is displayed in the both pixels, as shown in FIG. 16. According to the configuration described above, the same image is reflected onto the both eyes, and it is possible to make the viewer recognize a two-dimensional image.
The method described in the Patent Document 1 has a defect that it is required to sacrifice a half of a screen resolution in displaying a two-dimensional image in order to display both of a two-dimensional image and a three-dimensional image. In a normal display device for displaying only a two-dimensional image, a corresponding image can be displayed with respective to each of all pixels. In the display device disclosed in the Patent Document 1, however, as understood from FIG. 16, images of all the pixels cannot be reflected on the both eyes unless the same image is displayed in the pixel for left eye and the pixel for right eye. If a corresponding image can be displayed with respective to each of all the pixels to ensure the resolution in displaying a two-dimensional image, images of all the pixels are not reflected on the both eyes to see a fuzzy image. Accordingly, when priority is placed on the image quality, a half of the resolution is forced to be necessarily sacrificed.
In general display devices, a two-dimensional image is crushingly frequently displayed more than a three-dimensional image, and it is not desirable to sacrifice a resolution of a two-dimensional image for providing a function of displaying a three-dimensional image.
Consequently, Non-Patent Document 1 discloses a technique for displaying a three-dimensional image, which is developed in order to avoid the defect.
Non-Patent Document 1: Naoki TANAKA, “LIQUID CRYSTAL DISPLAY FOR SELLING PC AND MOBILE PHONES MORE INEXPENSIVE”, NIKKEI MICRO DEVICES (October 1st), JAPAN, Nikkei Business Publications, Inc., published on Oct. 1, 2002, No. 208, pp 91-96
The technique for displaying a three-dimensional image, which is described in the Non-Patent Document 1 above, will be described in detail with reference to FIGS. 17 and 18. FIGS. 17 and 18 are diagrams showing a positional relationship of a pixel of a liquid crystal panel 1601, a retardation film 1602, a liquid crystal for switching 1603, a polarizing plate 1606, and both eyes of a viewer.
Of a plurality of pixels of the liquid crystal panel 1601, FIGS. 17 and 18 show only sections of a line of pixels in the direction along a line connecting the both eyes, similarly to FIGS. 15 and 16.
In the retardation film 1602, two regions that have 90° different directions of polarization from each other are arranged in stripes, and each of the regions has a longitudinal direction that corresponds to a perpendicular direction to the direction along the line connecting the both eyes in a plane parallel to the liquid crystal panel 1601. In addition, the polarizing plate 1606 has a direction of polarization, which is mutually ±45° different from those of the two regions of the retardation film 1602.
On the opposite side of the liquid crystal panel 1601 from the viewer, the retardation film 1602, the liquid crystal for switching 1603, and the polarizing plate 1606 are provided and the retardation film 1602 is interposed between the liquid crystal panel 1601 and the liquid crystal for switching 1603. In addition, the polarizing plate 1606 is provided on the opposite side of the liquid crystal for switching 1603 from the retardation film 1602.
Further, a light guiding plate 1604 is provided on the further other side of the polarizing plate 1606 from the viewer. Light emitted from a light source 1605 is made to travel in the light guiding plate 1604 and irradiated to the polarizing plate 1606. The polarizing plate 1606 transmits predetermined polarized light of the irradiated light. The transmitted light is made incident into the liquid crystal for switching 1603.
The liquid crystal for switching 1603 can rotate a plane of polarization of transmitting light when the liquid crystal has an orientation controlled by voltage. When a three-dimensional image is displayed as shown in FIG. 17, a plane of polarization of transmitting light is rotated 45° in the liquid crystal for switching 1603. The light with the plane of polarization rotated 45° is transmitted through either of the two regions of the retardation film 1602.
In this way, the combination of the retardation film 1602, the liquid crystal for switching 1603, and the polarizing plate 1606 can function as a parallax barrier.
When the light transmitted through the retardation film 1602 is transmitted through the liquid crystal panel 1601, it is possible to make light from a pixel for right eye incident only into the right eye and to make light from a pixel for left eye only incident into the left eye. In the result, it is possible to make the viewer recognize a three-dimensional image formed of the image L and the image R.
In the case of displaying a two-dimensional image, the plane of polarization is not rotated in the liquid crystal for switching 1603. Therefore, approximately a half of light transmitted through the polarization plate is transmitted uniformly through the two regions of the retardation film 1602. The configuration described above makes it possible to reflect images of all the pixels onto the both eyes of the viewer, and a two-dimensional image can be recognized without sacrificing a half of the resolution unlike the Patent Document 1.
However, since it is required to provide the liquid crystal for switching in addition to the liquid crystal panel in the method described in the Non-Patent Document 1, the display device itself is bulky to hinder making a thin shape.